Games and various sports activities have been a part of civilization for most of recorded time and have, in fact, grown dramatically in popularity in the United States and around the world over the last century. Many types of playing surfaces have been developed to provide a suitable surface on which to conduct these various sports activities.
One of the first of such playing surfaces was a natural grass surface. Grass fields offer several advantages for conducting different types of games and related activities. For instance, natural grass fields provide an excellent shock-absorbing cushion for athletes as they run, jump and dive their way to victory over their opponents. This is an important aspect of any playing surface, since it is well known that the athlete's bones, joints and body, in general, absorb a great deal of shock force when impacting the playing surface while performing various athletic maneuvers. Maximum absorption of shock forces helps to reduce injuries that may arise when the athlete's body is subjected to shock forces over time.
Another advantage grass fields offer is that they provide excellent traction in dry weather conditions, allowing the athlete to keep proper balance and thereby more properly execute athletic maneuvers.
A further advantage grass fields offer is that they contain moisture in their grass root systems. The moisture functions in two ways. First, the moisture acts as a natural heat dissipator that, in turn, provide a relatively cool surface on which to perform the physically demanding activities. Second, the moisture functions as a lubricant to provides an appropriate amount of friction co-efficient reduction to prevent "footlock"--a situation that arises when the athlete's shoe momentarily sticks or drags on the turf, sometimes causing the athlete to stumble or fall. This second function also helps to prevent immediate injuries, because, when the athlete is hit by another player, the moisture in the grass surface allows the athlete's foot to slide across the surface instead of sticking to the surface. This lubricating action greatly reduces the chance of injury to the legs, and particularly to the knees or ankles. Additionally, natural grass fields absorb and drain water to an acceptable degree.
To this point, the discussion has been directed primarily to applications of grass fields in playing sports such as baseball, football, soccer or other outdoors sports that require a playing field. In addition to these applications, however, grass turf is also applicable in a golf course setting. The reason is that the various grass turfs customarily found on golf courses offer an ideal playing surface. For instance, the moisture content of the greens gives the right amount of ball stopping control as a ball is hit onto the green. Also, putting is affected by the amount of moisture available in the turf. Additionally, the impact absorption capability is a significant factor in properly stopping an in-flight ball on the green. While grass fields and turfs have several advantages and applications, there are, unfortunately, certain disadvantages associated with grass fields and turf.
One such disadvantage is that grass fields, of course, become very muddy and slippery when exposed to large amounts of water in a short period of time and, when excessively wet, they can be torn up rather quickly. Another disadvantage is that many of today's sports arenas are domed and enclosed for year round comfort of the spectators and the athletes alike. As such, natural grass fields are less desirable in these enclosed areas because of inadequate exposure to sunlight. Still another disadvantage is that grass fields require constant watering, fertilizing and general maintenance to keep them in an ideal playing condition. This upkeep is very expensive in that it requires substantial amounts of time and money for maintenance crews and supplies.
With respect to applications involving golf courses, the natural grass turf also has the same disadvantages regarding upkeep and general maintenance with even more cost and time involved. For example, tee boxes undergo regular abuse as successive golfers make divots in the surface of the turf while teeing-off from the box. The boxes, therefore, require constant replacement of sod and turf and, in some cases, require the provision of more than one tee box for each hole. Another example is the damage that occurs to greens when the balls impact the green and the physical damage that is often done by golfers and harsh weather conditions. Finally, grass and especially green grass can be very susceptible to frost damage, fungus and various other types of environmental conditions.
Another type of artificial turf that has been extensively used over the last two decades is "ASTRO TURF.RTM.", which is comprised of strands of extruded plastic. The "ASTRO TURF.RTM." is laid over a shock absorbing underlayment and a foundational hard base. Other types of artificial turfs include loop-pile carpet-like turfs, knitted nylon or polypropylene turfs or polypropylene tufted turfs.
The foundational hard base conventionally consists of a stone material that may vary in depth, depending on the intended use. The hard base is normally formed by depositing the stone material in a layer of at least six inches deep to a tolerance of plus or minus one inch and sloped in a predetermined direction for water drainage. The layer is then compacted, watered for optimum moisture content, and rolled to a compaction rate of 95% standard procter density. The compacted stone material is then normally oiled with a primer of hot, liquid asphalt to seal the material and provide bonding for subsequent deposition of an asphalt layer on top. Next, hot-mix asphalt is laid in place by conventional paving equipment. On top of this asphalt is laid a conventional underlayment or shock pad over which the artificial turf is laid.
Conventional underlayment shock pads typically consist of a hardened mixture of rubber granules and either a polyurethane, polyethylene or polyvinyl chloride binder in combination with a small pebble or stone approximately 4 to 9 mm in diameter. The conventional mixture forms what is known as a "closed cell" system, where multitudes of noncontiguous air pockets are trapped in the mixture. These pads average 5/8 inches in thickness when laid over the hard base asphalt. While the combination of the artificial turf and the underlying shock pad overcome some of the disadvantages associated with the natural grass field or turf, they introduce, however, several other disadvantages.
One such disadvantage is that many of the conventional shock pads are closed-cell systems. Again, a closed cell system is one in which the cells within the pad structure are not interconnected with one another or the surface of the pad. As such, the pad cannot "breathe", i.e, water and air cannot move into and out of the pad. In fact, the typical closed-cell system pad is specifically designed to repel moisture to enhance the water shedding capabilities of the playing surface in general. Thus, the pad neither retains moisture nor allows moisture to pass therethrough. This is a significant disadvantage because there is no moisture present to act as a natural lubricant, thereby preventing footlock, or to act as a natural heat dissipator, thereby providing a cooler playing surface.
Another disadvantage of the closed-cell system is that the closed-cell pads collapse over time, increasing the shock to the athlete, in turn transmitting greater shock to the athlete's body upon impact. Furthermore, the pads are initially limited in shock absorption, especially from greater heights, which, of course, increases the amount of force that the athlete's body absorbs when it impacts the surface.
Still another disadvantage of the prior art shock pads is that they use a polyurethane foam that causes the pad to be too rigid and hard. This rigidity and hardness detracts further still from the pad's ability to absorb the appropriate amount of impact shock. In addition, pebbles or stones are usually incorporated making the pad even harder still and thus even less capable of absorbing the appropriate amount of impact shock.
While some open-celled systems do exist, they also suffer from disadvantages. For example, as with closed-celled systems, open-celled systems typically include pebbles or stones and polyurethane foams in the mixture. As previously stated, polyurethane foams cause the pad to become hard and less absorbent over time. In addition, moisture cannot be entrained or entrapped within the pad because the pads are typically designed to allow water to pass through them to drain water effectively from the playing surface. Thus, footlock and a high playing field temperature are also prevalent in these conventional open-celled systems as well.
Applications of the conventional underlayments discussed above with respect to golf courses are unsatisfactory for basically the same reasons. First, the base or shock pad does not contain enough moisture to effectively simulate a natural grass green regarding its ability to stop an in-flight ball landing on the green. Moreover, the pad lacks the required degree of energy absorption that is necessary to properly stop the ball and that is necessary for absorbing the impact of the golf club as the golfer hits the tee shot from the tee box.
Accordingly, what is needed in the art is a shock absorbing underlayment that is durable, absorbs shock in the manner of a natural grass field and retains moisture to lubricate the surface of the artificial turf to prevent footlock and provide a playing surface that is cooler. The shock pad of the present invention addresses these needs.